The present disclosure provides an apparatus and methods for installing and selectively retrieving a casing hanger locking device within a wellhead system during the bit run and retrieval operations.
Natural resources such as oil or gas residing in a subterranean formation can be recovered by drilling a wellbore that penetrates the formation. The drilling operation involves the use of a drill bit at the end of a drill string to cut through the ground and drill the wellbore. A drilling fluid may be circulated downwardly through the drill string and then upwardly through the wellbore to the surface. The drilling fluid may be used to, among other things, cool the drill bit, lubricate the rotating drill string to prevent it from sticking to the walls of the wellbore, and remove drill cuttings from the wellbore.
During the drilling operations, the wellbore passes through subterranean formations with a variety of geological characteristics. Many of these subterranean formations contain fluids, including water and hydrocarbons, known as formation fluids. The formation fluids often exist at high temperatures and pressures. In certain circumstances, the high temperatures and pressures in the subterranean formation lead to upward loads and/or forces that require the pressures of the formation fluids to be controlled.
In ideal circumstances, the pressures of the formation fluids may be controlled by balancing the pressure of the formation fluid with the hydrostatic pressure of a drilling fluid. The weight of the drilling fluid, which can be adjusted by adding weighting agents, is usually sufficient to control the subterranean pressure and prevent the upward loads.
The subterranean pressures can change, however, and sometimes these changes can be sudden and unpredictable. For example, if the drill bit penetrates a formation with a higher pressure, the hydrostatic pressure of the drilling fluid may not be sufficient to balance this increased pressure of the formation fluid. In certain instances, this can lead to a blowout. Blowouts lead to loss of pressure control and possible heat transfer of (uncontrolled) fluid. These aspects in turn lead to increased annulus pressure, thermal growth which leads to mechanical loads, and direct mechanical loads.
Steps must be taken to control the upward loads from the formation fluids in the subterranean formation and the wellbore during the drilling operation. If these steps are not taken, the upward load can unseat the casing hanger used in the wellbore. This may result in the possible failure of the casing hanger annulus seal, which can lead to further loss of pressure control. Unseating the casing hanger can also create mechanical interference with separate pressure control or containment devices. The failure to control the upward loads in the wellbore can lead to loss of operator control in the drilling operations, damage to the drilling equipment, and even injury to the personnel on site.
Mechanical locking devices are used to control the upward loads and prevent the upward travel of the casing hanger in a blowout condition or similar condition. The locking devices are typically installed at the top of the casing hanger at the wellhead. The locking devices are designed to resist upward loads so that the casing hanger does not travel upward through the wellbore even if the subterranean pressure spikes. Thus, even when subterranean fluids flow upward, the casing hanger remains locked in place and does not interfere with the pressure control and containment devices.
Locking devices can be difficult and expensive to use, however. For example, subsequent casing runs cannot be made with the locking device installed in the wellhead because the locking device interfaces with many of the same components with which the next casing hanger would interface. As a result, the locking device must be removed from the wellbore each time casing is added. Conventional locking devices require a dedicated trip to run and retrieve, and three total trips are required to use a conventional locking device. The first trip is typically a measurement trip to verify the position of the most previously installed casing hanger. The second trip is typically the installation of the locking device. And the third trip is typically the retrieval of the locking device. These trips can be substantial, particularly in subsea drilling operations, where the wellhead may be located thousands of feet below the ocean surface. Each trip requires dedicated tooling to perform the intended task, and at current rig rates, these operations become very expensive.